It seems to me this signage thing is pretty simple though: if you're carry a firearm, whether concealed or open, you are always on the lookout for signage. So if you see a sign, ANY sign including one that says simply "no guns", if you walk-in OC you are asking for trouble. If you walk-in anyway, CC, then you must be very confident that you are concealed.
My understanding of the standard signs, especially the 1" tall letter requirement, is that this is intended so people see the sign! And since carriers are looking in the first place, they will surely see it unless it is simply not present near the door they enter. Very small signs, or hand-written signs should be obeyed if you can see-and-read them, but if you don't/can't then the law protects you from prosecution.